Medications that Cause Constipation in Dogs

Some medications can cause constipation in dogs, the result of a side effect to medication taken for some other medical condition. Some of these medications include antihistamines, antacids, diuretics and iron supplements.

Signs and Symptoms

Poor diet as well as medications can bring about constipation in dogs. Symptoms of constipation include:

  • Infrequent bowel movements
  • Straining to have a bowel movement, perhaps accompanied with whimpering
  • Passing a small amount of fecal matter or nothing at all
  • Passing hard, dry fecal matter
  • Passing liquid feces after prolonged straining

Any of the above can be accompanied with a lack or loss of appetite, depression or vomiting. If your dog has become constipated after taking medication, check the drug's warning label to see if constipation is one of the possible side effects.

Medications that Cause Constipation

  • Antihistamines
    Antihistamines are prescribed for treatment of allergies in dogs. The most commonly used antihistamines are: Benadryl, Atarax, Tavist, Seldane and Chlortrimeton.
  • Antacids
    Antacids are used under the direction of a veterinarian for the treatment of stomach disorders, ulcers, heartburn and to lower high phosphorous levels in dogs with kidney failure.
  • Diuretics
    Diuretics are used to treat congestive heart failure in dogs by removing the pooled fluids and blood in the organs and lungs. Congestive heart failure occurs when the heart cannot properly circulate the blood in the body, so there is increased back pressure and decreased effectiveness with the heart acting as a pump. This causes the heart to enlarge and fluids to accumulate inside and around the heart and lungs. The belly also tends to swell. Diuretics, such as furosemide (Lasix) and spironolactone are commonly used to treat this disease.
  • Iron Supplements
    Iron supplements are used to treat anemia and iron deficiencies in dogs. This can be a result of a loss of blood, parasites, urinary tract infection, stomach or intestinal mass or lymphoma.


Probiotics are live microorganisms that can restore the critical natural flora found in the intestine that are necessary for proper bowel movements. Antibiotics strip the intestines of healthy bacteria as it is killing the infection and bad bacteria. Usually treatment lasts for up to two weeks after the last use of the antibiotics.

Stool softeners help to restore moisture in the stool, making it softer and easier to pass. Lubricates, such as mineral oil, also hydrate the colon and stimulate bowel movements. Another method in hydrating the colon is the use of an enema. Human enemas are not to be used on dogs, so it may be necessary to visit a veterinarian for its administration. The use of fiber in your dog's diet can treat constipation. Fiber absorbs water, bulking up the contents in the intestine and thereby stimulating a bowel movement.

Constipation Can Be Dangerous

It is very important to treat constipation as soon as possible, since it can lead to severe blockage, rupturing of the colon and possibly death. Surgery may even be necessary. After the administration or introduction of any medication, monitor your dog for any such side effects.